A polymer electrolyte fuel cell (PEFC) comprises a membrane known as a “MEA” comprising an anode and cathode formed by superimposing a catalyst and a gas diffusion electrode layer on both sides of a polymer electrolyte membrane, and a carbon or metal bipolar plate in which passages are formed for supplying fuel gas and oxidizing agent gas to these electrodes.
In order for the PEFC to generate power, the above polymer electrolyte membrane must contain moisture, so to ensure that the membrane retains moisture, the fuel gas and oxidizing agent gas supplied to the fuel cell are normally humidified. Pure water is also produced at the cathode when power is generated, so the oxidizing agent passage contains moisture. Normally, the fuel cell has a passage for circulating a cooling fluid to cool the heat which is generated, and pure water may be used as the cooling fluid. In a fuel cell where the gases are humidified and the water produced is recovered by interconnecting the cooling fluid passage, fuel gas passage and oxidizing agent gas passage via a porous member, the cooling fluid passage and porous member interior also contain water.
Therefore, water is contained in various parts of the fuel cell, and if the fuel cell is left for a long time in an environment below freezing point when it is not running, the water inside the fuel cell freezes. Hence, if the fuel cell is started from this state, the ice in the fuel cell must be thawed.
JP 2000-315514A published by the Japanese Patent Office in 2000 proposes a method of thawing the ice in the fuel cell by passing a hot gas into the fuel cell passages (fuel gas passage, oxidizing agent gas passage, cooling fluid passage).